This invention relates to hydroformed tubular structures including hydroformed joints at which members or parts of the structures are fixed to one another and to methods of making such hydroformed joints. In particular, the invention involves hydroformed conjugate joints, such as might be used in vehicle structures.
The application of hydroformed tubular components in vehicle structure assembly is attracting increasing interest in the automobile industry at this time. One of the important factors for successful applications of this technology is to effectively join two or more essentially closed box section components together in a manner which provides satisfactory structural performance as well as manufacturing and assembly efficiency.
Traditional joining methods for a typical lap joint are shown in FIGS. 1 and 2, and for a T-joint in FIGS. 3 and 4. These methods usually require relatively expensive secondary operations after the hydroforming process to end trim or cut the ends of the box sections of the joining members. A saw cut, plasma cut, or laser cut process is usually employed in these secondary operations which may involve significant tooling costs, require control of trimming quality and have excessive cycle time for completing these operations. In addition, the traditional hydroformed joint designs may have relatively weak stiffness of their box sections in resisting local buckling.
In a conventional lap joint 10 illustrated in FIGS. 1 and 2, a trimmed hydroformed end 12 of one member 14 is slid inside a trimmed hydroformed member 16 through a cutout 18 in a side 20 of the member 16. The assembled components 14, 16 are then fixed together, such as by through bolts or welding.
In a conventional T-joint 22 shown in FIGS. 3 and 4, one hydroformed tubular member 24 has opposite sides 26 cut out to form depending legs 28. In assembly, the legs 28 straddle opposite sides 30 of a second hydroformed tubular member 32 to form the T-joint 22, the members being preferably welded together. Both of these arrangements form box section structures with limited structural strength, particularly for bending and torsional loads.
The present invention provides improved joint structures for hydroformed tubular members in which the joint structures are formed by simplified manufacturing processes that reduce the cost of manufacturing. The strength of the resulting hydroformed tubular structure may also be increased.
For both lap joint and T-joint structures, a hydroformed tubular structure according to the invention connects at least two hydroformed members at a joint including, in at least one of the members, a flat portion at one end with an adjacent hydroformed conjugate portion. The conjugate portion is adapted to engage a recess in a second member and the flat portion is adapted to be secured to an adjacent portion of the second member.
In a preferred embodiment of a lap joint, two or more members having hydroformed conjugate ends may be formed from a single tubular member in a single hydroforming process. The resulting hydroformed ends each include a flattened portion offset toward one edge and having opposite sides smashed into engagement, and a hydroformed conjugate portion offset toward an opposite edge and having one side extending upward from the flat portion. The similarly formed ends are mated by having the raised conjugate portions of the two ends each engage the flat portions of the other member. The flat portions thus form the recesses in which the conjugate portions are received. The resulting joint may be held in assembly by bolts extending through openings in the conjugate portions and their associated flat portions or the joint may be secured by welding.
A method of making a hydroformed tubular structure with the lap joint as described above involves: placing in a hydroforming die a tubular member having opposite ends, filling the tubular member with hydroforming liquid prior to completely closing the die, flattening at least one portion of the tubular member between its ends by forcing opposite sides of the member into engagement upon completing closing of the die, and increasing the pressure of the liquid in the member to hydraulically expand or hydroform the member against the surrounding die to obtain a predetermined configuration. The hydroformed shape includes expanded conjugate portions adjacent the flattened portion. The engaged sides of the flattened portion must allow sufficient liquid flow therethrough to permit pressurizing the member from one of the ends. The flattened portions of the member are then trimmed to form a plurality of separated hydroformed parts, each having at least one flattened end portion with an adjacent expanded conjugate portion. Each joint is then formed by securing the flattened portion of a first one of the parts to a conjugate portion of a second part having a recess receiving the conjugate portion of the first part.
In forming a lap joint, the first and second parts may be formed from the same hydroformed member. The flattened portions are located at trimmed ends separated in the trimming step, the trimmed ends having interengaging expanded conjugate portions secured to the flattened portions of the other part to form the joint. In forming a T-joint, the first part includes a flattened end with an inwardly adjacent expanded conjugate portion and the second part is formed as a tubular hydroformed member with a recess in part of one side so that the flattened end is secured to that side adjacent the recess and the conjugate portion is received in the recess.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.